A smart key system allows a driver who is located outside a vehicle to open or close doors of the vehicle as well as to start the vehicle, although the driver does not insert an ignition key into a key box of the vehicle and does not perform a special manipulation for vehicle operation. Generally, a smart card capable of being easily carried by the driver and a smart key fob for wireless communication have been used for the smart key system.
If the driver who carries the smart key approaches the vehicle, a door lock is automatically released through Low Frequency (LF) and Radio Frequency (RF) communication with the smart key, such that the driver can easily open the doors without inserting a key into a keyhole of the door and can start the vehicle without insertion of the ignition key.
In more detail, the smart key system for use in vehicles includes a process of transmitting a search signal (LF frequency band) to search for the smart key located in the vicinity of the vehicle, and a process of receiving a search response signal (RF frequency band) from the smart key in response to the search signal.
The LF signal, having a relatively lower frequency band than the RF signal, has a limited transmission distance, such that the vehicle can receive the search response signal from the smart key only when the smart key is located close to the vehicle.
Therefore, in order to determine whether the smart key is located in the vicinity of the vehicle, the vehicle periodically transmits the search signal over the LF communication network. If the vehicle receives the search response signal from the smart key at a specific time, the vehicle communicates with the smart key.
On the other hand, the vehicle according to the conventional art periodically transmits the search signal to a peripheral region during a predetermined time during which the user does not use the vehicle, resulting in unnecessary power consumption of the vehicle.